This application relates to refrigeration systems and more particularly relates to energy saving refrigeration systems.
Household refrigerators typically operate on a simple vapor compression cycle. Such a cycle typically includes a compressor, a condenser, an expansion device, and an evaporator connected in series and charged with a refrigerant. The evaporator is a specific type of heat exchanger which transfers heat from air passing over the evaporator to refrigerant flowing through the evaporator, thereby causing the refrigerant to vaporize. The cooled air is then used to refrigerate one or more freezer or fresh food compartments.
In conventional single-evaporator refrigerators, since the freezer compartment and the fresh food compartment are simultaneously cooled with one evaporator, the temperature of the evaporator must be maintained at a temperature lower than about xe2x88x9215xc2x0 C., which is typically the temperature of the freezer compartment. Accordingly, an evaporator with a lower temperature than is necessary is used to cool the fresh food compartment, causing the efficiency of the overall system to be relatively low.
Other conventional refrigerators require at least two capillary tubes to control expansion. Each capillary tube is preceded in the refrigerant flow path by an electrically activated valve in order to control liquid discharge from the condenser to selectively flow through one of the capillary tubes. An air flow direction control scheme directs air flow to and from the sole evaporator to be either fresh food or freezer compartment air. When the air flow coupling is with the fresh food compartment (about 7xc2x0 C.) the refrigerant operates at a relatively high evaporator saturation temperature and when the air flow coupling is with the freezer compartment (about xe2x88x9215xc2x0 C.), the refrigerant operates at a relatively lower saturation temperature.
Higher evaporator refrigerant saturation temperature is desirable since the higher the saturation temperature, the greater the obtainable cycle efficiency. The cycle efficiency, however, will only be greater for higher temperatures if the evaporator exit state is such that the refrigerant is substantially a saturated vapor. Accordingly, this is the purpose for two switchable capillary tubes. A higher evaporator saturation temperature produces a high pressure, thus a higher vapor density, thereby generating a greater compressor mass flow rate. To support a higher compressor mass flow rate, a less restrictive capillary tube is required. This system will work satisfactorily near operating conditions for which the capillary tubes were optimized. At off design conditions, however, the evaporator exit state will be either a vapor quality or superheat and cycle efficiency will be lower.
Additionally, during operation of conventional refrigeration systems, condensed moisture forms as frost or ice on the exposed surfaces of an evaporator. Since ice accumulation will eventually cause cycle efficiency degradation, the evaporator must periodically undergo a defrosting period.
Therefore, it is apparent from the above that there exists a need in the art for a simplified refrigeration expansion control and for improved defrosting within refrigeration systems.
A refrigeration system disposed within an outer cabinet having a freezer compartment and a fresh food compartment comprises a freezer evaporator and a fresh food evaporator each having an inlet and an outlet. A compressor is coupled to the freezer evaporator via a conduit and a control valve is disposed at the inlet of the freezer evaporator to control refrigerant flow therethrough. A first liquid line temperature sensor is disposed so as to detect refrigerant temperature at the inlet of the freezer evaporator and a second liquid line temperature sensor is disposed so as to detect refrigerant temperature at the inlet of the fresh food evaporator. A freezer compartment temperature sensor and a fresh food compartment temperature sensor are disposed within the freezer compartment and the fresh food compartment, respectively, to sense compartment temperatures. A controller is coupled to the control valve and to the compressor so as to provide control signals thereto and to the liquid line temperature sensors and the compartment temperature sensors to receive temperature signals therefrom. The controller generates control signals to the control valve in response to temperature signals generated from the liquid line temperature sensors and the compartment temperature sensors to modify the control valves duty cycle of open-to-closed conditions so as to maintain evaporator dryness at a relatively fixed level.